The iOS 9.3 update for all the compatible iDevice is now available and if you are having trouble in updating the device via Over the Air download due to various problems, then you shouldn't be dejected because there is alternative method available to update your device.
- First make sure that you have the latest version of iTunes is installed on your Mac or Windows PC.
- If you haven't download iTunes, then get it for free from Apple website.
- Now download the IPSW file corresponding to your device from here.
- Now turn off 'Find my iPhone' from Settings > iCloud.
- Connect your device to PC using USB cable and take full Backup/Sync your device.
- Press the Shift Key on Windows [Option key on Mac] on your keyboard and click Restore in iTunes.
- Release the Shift/Option key and browse through the downloaded IPSW file.
- Select the IPSW file and click on Update.
Wait until the process finishes. Once the process is completed, you need to restore your device from the Backup that was taken earlier.